1. Field of the Invention
The present invention relates to exhaust gas filters for collecting fine particles comprising, as a main component, carbon, being contained in exhaust gases of internal combustion engines or the like (hereinafter referred to as "internal combustion engines") and removing deposits of the particles by means of gas streams counter to exhaust gas flow.
2. Description of the Prior Art
Exhaust gases from diesel engines contain fine particles comprising, as a main component, carbon in a high concentration, which cause environmental disruption, such as air pollution or the like. Japanese Utility Model Publication No. 10422/'87 discloses various exhaust gas filters for collecting and removing such fine particles contained in the diesel engine exhaust gases.
The filters disclosed in the above Utility Model Publication comprise a honeycomb structure in which honeycomb-cells for gas flow passage are divided into two groups: the first group of the cells each having its rear aperture plugged up and the second group of the cells each having its front aperture plugged up, with a sealing member. In the first group, each of the cells is plugged up with a sealing member which has through-pores of small diameters formed therein so as to allow exhaust gases to pass. With the exhaust gas filters of such a structure, fine particles contained in exhaust gases are collected on thin partition walls defining gas flow passages, while incombustible components of larger diameters, contained in the exhaust gases, are discharged from the through-pores provided on the sealing members of the first cell group to outside the filter. Consequently, since only combustible fine particles deposit inside the filter, the collected fine particles can be removed by burning up by means of periodically igniting of the filter.
However, such conventional exhaust gas filters pose a problem in that not only do these filters require a means for collecting incombustible particles discharged through the through-pores to the outside of the filters, but also, even though the through-pores are provided in the sealing members, blocking of the thin partition walls of the filters is increased as the deposits are built up right below the sealing members in the first cell group and, in addition, the fine particles collected in the filter can not completely be removed by ignition.
It would be assumable that such a problem could be solved by intermittently injecting blowback air counter to exhaust gas flow, from the sealed side of the first cell group, to thereby release the fine particles or incombustible particles deposited on the inner walls of the filter and then treating the released deposits. However, this treating technique raises another problem such that the blowback air can remove particles only within a very narrow range right below the through-pores, so that the most part of the built-up deposits remains.